Method for the production of a rim for a can lid

ABSTRACT

In a process for production of a lid ring ( 30 ) which can be connected to the can body, which borders a discharge opening ( 38 ) and has a heat-sealable coating ( 40 ) on which to form a can lid ( 50 ) a closing membrane ( 44 ) can be heat-sealed covering the discharge opening ( 38 ), a metal strip ( 12 ) with parallel side edges ( 14, 16 ) is formed into a tube ( 20 ) and the side edges ( 14, 16 ) are welded or glued parallel to the tube longitudinal axis (x). The tube ( 20 ) produced in this way is divided into tube sections ( 24 ) of equal length with cut edges ( 26, 28 ) lying in parallel planes. The tube sections ( 24 ) are formed into lid rings ( 30 ) where a first cut edge ( 26 ) is formed into an outer rim ( 32 ) for connection to a can body and the second cut edge ( 28 ) is curled away from the side intended for the heat-sealable coating ( 40 ). The heat-sealable coating ( 40 ) is applied to the finished molded lid ring.

This is a 371 national stage application of International (PCT) PatentApplication No. PCT/EP2004/00128, filed on Jan. 12, 2004, that hasbenefit of the priority of European Patent Application No. 03405014.6,filed on Jan. 16, 2003.

FIELD OF THE INVENTION

The invention concerns a process for production of a lid ring which canbe connected to a can body, which borders a discharge opening and has aheat-sealable coating, on which to form a can lid a closing membrane canbe heat-sealed covering the discharge opening, in which process a sheetmetal strip with parallel side edges is formed into a tube and the sideedges are welded or glued parallel to the tube longitudinal axis, thetube produced in this way is divided into tube sections of equal lengthwith cut edges lying in parallel planes, and the tube sections areformed into lid rings, where a first cut edge is formed into an outerrim for connection with a can body and the second cut edge is curled.

BACKGROUND OF THE INVENTION

In known can lids with a lid ring and a closing membrane arrangedthereon, the discharge opening extends up to the vicinity of the outerrim so that after removing the closing membrane, usually formed as atear film, only a narrow ring surface remains radially adjacent on theinside to the outer rim. After removing (peeling) the membrane, as in afully tear-off lid, a relatively large container opening results throughwhich the filling is easily accessible. A further advantage of this lidsystem is that the filling can be sterilized.

In a process known from EP-A-1 153 840 for production of a lid ring fora can lid with closing membrane, first a flat sheet metal part with aheat-sealable coating on one side is formed into a cylindrical tube, thecoating being on the inside. The axial edges of the tube are pressed andwelded together, which can be achieved by means of a laser beam andleads to the formation of a butt weld seam. The tube is then dividedinto tube sections or cylindrical rings of equal length. Eachcylindrical ring is formed into a lid ring with an outer rim forattachment to a can body and into an annular support surface forsubsequent fixing of the closing membrane. Here, the edge bordering thelater discharge opening is curled against the side with theheat-sealable coating.

The process described above for production of a lid ring starting from acylindrical ring has the advantage of a considerable reduction in theamount of waste in comparison with the conventional method of lid ringproduction in which first a metal disc is molded and then the dischargeopening punched out to form the lid ring.

In the process described in EP-A-1 153 840, it must be ensured that, onforming the butt weld seam, the adjacent heat-sealable coating is notdamaged. For this, during the welding process a cooling plate is pressedagainst the inside of the tube along the axial edges. Despite thesemeasures damage to the heat seal layer can never be completely excluded.As the heat seal layer also serves as corrosion protection, corrosioncan occur later at damaged points on the weld seam.

SUMMARY OF THE INVENTION

The invention is based on the object of refining a process of the typecited initially so that optimum corrosion protection can be achieved.

To achieve the object according to the invention, the second cut edge iscurled away from the side intended for the heat-sealable coating, andthe heat-sealable coating is applied to the finished molded lid ring.

The subsequent coating of the lid ring according to the inventioneliminates the corrosion problem which occurs in the process accordingto the prior art.

Suitable metals for performance of the process according to theinvention are all metals known for the production of cans or lid ringssuch as aluminium, steel or tin plate.

Preferably, the parallel side edges of the metal strip are pressedtogether into a butt joint and welded by means of a laser beam to form atube.

The heat-sealable coating can be sprayed onto the lid ring dissolved ina solvent in the known manner, or be applied to the lid ring by powdercoating in powder form e.g. as a polypropylene powder.

In a preferred embodiment of the process according to the invention, thelid ring is coated with a heat-resistant lacquer on its side facing awayfrom the heat-sealable coating. Suitably, the heat-resistant lacquer issprayed onto the lid ring.

The tubes can be made of metal strip sections in the form of precutformats and independently of this divided into the individual tubesections.

The process according to the invention is particularly suitable forcontinuous production of lid rings. In a continuous production processthe metal strip is present in the form of rolled goods as a coil and isformed into a tube continuously by rolling. The tube sections arecontinuously separated from the tube at a cycle rate corresponding tothe speed of the tube length produced per time unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention arise from thedescription below of preferred embodiment examples and the drawing; thisshows diagrammatically:

In the drawings:

FIG. 1 is a side view of a plant for continuous production of tubesections;

FIG. 2 is a top view onto the plant in FIG. 1;

FIG. 3 is an oblique view onto a tube section;

FIG. 4 is a partly cut-away side view of a lid ring produced from thetube section in FIG. 3;

FIG. 5 is the lid ring in FIG. 4 coated on both sides; and

FIG. 6 is the lid ring of FIG. 5 with the closing membrane sealed on.

DETAILED DESCRIPTION OF THE INVENTION

In a process shown in FIGS. 1 and 2, a strip wound into a coil 10 asrolled product in the form of a metal strip 12 with parallel side edges14, 16 is unwound from the coil 10 and formed continuously into a tubeby rolling in the conveyor direction x. Here, the parallel side edges14, 16 of the metal strip 12 are pressed together into a butt joint andwelded together by means of a laser beam 18 into a tube 20 forming alongitudinal weld seam 21. The tube 20 is then divided in a cutting orseparating device 22 into tube sections of equal length in the form ofcylindrical rings 24 of equal height h.

A cylindrical ring 24 shown in FIG. 3, the periphery of whichsubstantially corresponds to the width b of the metal strip 12, isformed in the known manner into the lid ring 30 shown in FIG. 4 byseveral successive forming operations.

The lid ring 30 has a conventional outer rim 32, the free end of whichcorresponds to a first cut edge 26 of the cylindrical ring 24. The outerrim 32 transforms into a horizontal ring surface 34. The inner edge 36of the ring surface 34 bordering the discharge opening 38 is curled toeliminate risk of injury and to increase the rigidity of the lid ring 30with the edge angled radially outwards, which corresponds to the secondcut edge 28 of the cylindrical ring 24. The inner edge 36 of thehorizontal ring surface 34 is curled such that the second cut edge 28 ofthe cylindrical ring 24 comes to lie on the side later facing the insideof the can.

By way of spray devices 52, 54 the lid ring 30, on what will become itsoutside 56, is fitted with the heat-sealable coating 40 and on the sidewhich will later face the can interior, with a heat-resistant lacquercoating 42. On the inside 58 of the outer rim 32 is also applied asealant 48. The sprayed layers 40, 42 and sealant 48 are normally driedin an oven.

FIG. 6 shows the lid ring 30 with a closing membrane 44. The closingmembrane 44 which also has a heat-sealable coating e.g. polypropylene,is sealed against the heat-sealable coating 40 of the lid ring 30 andthus forms a can lid which is easy to open. The closing membrane 44 canbe fitted with a tear tab 46. In this case the seal between the closingmembrane 44 and the ring surface 34 is set such that the closingmembrane can be removed from the ring surface or the seal edge bypeeling. In an alternative embodiment the closing membrane 34 isconnected inseparably with the lid ring 30. In this case the membrane ispierced for opening and removed from the lid ring 30 along the inneredge of the ring surface 34.

The lid ring 30 fitted with the closing membrane 44 is flanged onto acan body as a can lid 50 after the can has been filled with a product.The filling can however also be placed in a can body which has beenpreviously fitted with a lid ring 30. In this case as the final step theclosing membrane 44 is sealed onto the lid ring 30.

1. A process for production of a lid ring (30), that can be connected toa can body, and that borders a discharge opening (38) and has aheat-sealable coating (40), on which to form a can lid (50) a closingmembrane (44) can be heat-sealed covering the discharge opening (38), inwhich process a metal strip (12) with parallel side edges (14, 16) isformed into a tube (20) and the side edges (14, 16) are welded or gluedparallel to the tube longitudinal axis (x), the tube (20) is dividedinto tube sections (24) of equal length with cut edges (26, 28) lying inparallel planes, and the tube sections (24) are molded into lid rings(30), where a first cut edge (26) is formed into an outer rim (32) forconnection with the can body and a second cut edge (28) is curled, thesecond cut edge (28) is curled away from a side (56) of the lid ring(30) intended for the heat-sealable coating (40), the heat-sealablecoating (40) is applied to the side (56) of the finished molded lid ring(30) intended to be outside of the finished molded lid ring (30), and aheat-sealable lacquer coating (42) is applied to side (58) of thefinished molded lid ring (30) intended to face interior of the can body.2. The process according to claim 1, wherein the metal strip (12)comprises aluminum, steel or tin plate.
 3. The process according toclaim 1, wherein the parallel side edges (14, 16) of the metal strip(12) are pressed together in a butt joint and welded into the tube (20)by means of laser beam (18).
 4. The process according to claim 1,wherein the heat-resistant lacquer (42) is sprayed onto the lid ring(30).
 5. The process according to claim 1, wherein the metal strip (12)is formed into the tube (20) as a precut format and welded.
 6. Theprocess according to claim 1, wherein the metal strip (12) is present asa coil (10) and is continuously formed into the tube (20).
 7. Theprocess according to claim 6, wherein the tube sections (24) arecontinuously separated from the tube (20) at a cycle rate correspondingto the speed of the tube length produced per time unit.
 8. The processaccording to claim 2, wherein the parallel side edges (14,16) of themetal strip (12) are pressed together in a butt joint and welded intothe tube (20) by means of laser beam (18).
 9. The process according toclaim 4, wherein the metal strip (12) is formed into the tube (20) as aprecut format and welded.
 10. The process according to claim 4, whereinthe metal strip (12) is present as a coil (10) and is continuouslyformed into the tube (20).
 11. A process for production of a lid ring(30) that can be connected to a can body, and that borders a dischargeopening (38) and has a heat-sealable coating (40), on which to form acan lid (50) a closing membrane (44) can be heat-sealed covering thedischarge opening (38), in which process a metal strip (12) withparallel side edges (14, 16) is formed into a tube (20) and the sideedges (14, 16) are welded or glued parallel to the tube longitudinalaxis (x), the tube (20) is divided into tube sections (24) of equallength with cut edges (26, 28) lying in parallel planes, and the tubesections (24) are molded into lid rings (30), where a first cut edge(26) is formed into an outer rim (32) for connection with the can bodyand a second cut edge (28) is curled, the second cut edge (28) is curledaway from side (56) of the lid ring (30) intended for the heat-sealablecoating (40), and the heat-sealable coating (40) is sprayed onto theside (56) of the finished molded lid ring (30) intended to be outside ofthe finished molded lid ring (30).
 12. A process for production of a lidring (30), that can be connected to a can body, and that borders adischarge opening (38) and has a heat-sealable coating (40), on which toform a can lid (50) a closing membrane (44) can be heat-sealed coveringthe discharge opening (38), in which process a metal strip (12) withparallel side edges (14, 16) is formed into a tube (20) and the sideedges (14, 16) are welded or glued parallel to the tube longitudinalaxis (x), the tube (20) is divided into tube sections (24) of equallength with cut edges (26, 28) lying in parallel planes, and the tubesections (24) are molded into lid rings (30), where a first cut edge(26) is formed into an outer rim (32) for connection with the can bodyand a second cut edge (28) is curled, the second cut edge (28) is curledaway from a side (56) of the lid ring (30) intended for theheat-sealable coating (40), and the heat-sealable coating (40) isapplied as a powder coating to the side (56) of the finished molded lidring (30) intended to be outside of the finished molded lid ring (30).13. The process according to claim 12, wherein the lid ring (30) iscoated with a heat-resistant lacquer (42) on it side facing away fromthe heat-sealable coating (40).
 14. The process according to claim 13,wherein the heat-resistant lacquer (42) is sprayed onto the lid ring(30).
 15. A process for production of a lid ring (30), that can beconnected to a can body, and that borders a discharge opening (38) andhas a heat-sealable coating (40), on which to form a can lid (50) aclosing membrane (44) can be heat-sealed covering the discharge opening(38), in which process the metal strip (12), comprised of aluminum,steel or tin plate, with parallel side edges (14, 16) is formed into atube (20) and the side edges (14, 16) are welded or glued parallel tothe tube longitudinal axis (x), the tube (20) is divided into tubesections (24) of equal length with cut edges (26, 28) lying in parallelplanes, and the tube sections (24) are molded into lid rings (30), wherea first cut edge (26) is formed into an outer rim (32) for connectionwith the can body and the second cut edge (28) is curled, the second cutedge (28) is curled away from a side (56) of the lid ring (30) intendedfor the heat-sealable coating (40), and the heat-sealable coating (40)is sprayed onto the side (56) of the finished molded lid ring (30)intended to be outside of the finished molded lid ring (30).
 16. Aprocess for production of a lid ring (30), that can be connected to acan body, and that borders a discharge opening (38) and has aheat-sealable coating (40), on which to form a can lid (50) a closingmembrane (44) can be heat-sealed covering the discharge opening (38), inwhich process the metal strip (12), comprised of aluminum, steel or tinplate, with parallel side edges (14, 16) is formed into a tube (20) andthe parallel side edges (14, 16) of the metal strip (12) are pressedtogether in a butt joint into the tube (20) longitudinal axis (x) bymeans of laser beam (18), the tube (20) is divided into tube sections(24) of equal length with cut edges (26, 28) lying in parallel planes,and the tube sections (24) are molded into lid rings (30), where a firstcut edge (26) is formed into an outer rim (32) for connection with thecan body and the second cut edge (28) is curled, the second cut edge(28) is curled away from a side (56) of the lid ring (30) intended forthe heat-sealable coating (40), and the heat-sealable coating (40) issprayed onto the side (56) of the finished molded lid ring (30) intendedto be outside of the finished molded lid ring (30).
 17. A process forproduction of a lid ring (30), that can be connected to a can body, andthat borders a discharge opening (38) and has a heat-sealable coating(40), on which to form a can lid (50) a closing membrane (44) can beheat-sealed covering the discharge opening (38), in which process themetal strip (12), comprised of aluminum, steel or tin plate, withparallel side edges (14, 16) is formed into a tube (20) and the sideedges (14, 16) are welded or glued parallel to the tube longitudinalaxis (x) the tube (20) is divided into tube sections (24) of equallength with cut edges (26, 28) lying in parallel planes, and the tubesections (24) are molded into lid rings (30), where a first cut edge(26) is formed into an outer rim (32) for connection with the can bodyand the second cut edge (28) is curled, the second cut edge (28) iscurled away from a side (56) of the lid ring (30) intended for theheat-sealable coating (40), and the heat-sealable coating (40) isapplied as a powder coating to the side (56) of the finished molded lidring (30) intended to be outside of the finished molded lid ring (30).18. A process for production of a lid ring (30), that can be connectedto a can body, and that borders a discharge opening (38) and has aheat-sealable coating (40), on which to form a can lid (50) a closingmembrane (44) can be heat-sealed covering the discharge opening (38), inwhich process the metal strip (12), comprised of aluminum, steel or tinplate, with parallel side edges (14, 16) is formed into a tube (20) andthe parallel side edges (14, 16) of the metal strip (12) are pressedtogether in a butt joint into the tube (20) longitudinal axis (x) bymeans of laser beam (18), the tube (20) is divided into tube sections(24) of equal length with cut edges (26, 28) lying in parallel planes,and the tube sections (24) are molded into lid rings (30), where a firstcut edge (26) is formed into an outer rim (32) for connection with thecan body and the second cut edge (28) is curled, the second cut edge(28) is curled away from a side (56) of the lid ring (30) intended forthe heat-sealable coating (40), and the heat-sealable coating (40) isapplied as a powder coating to the side (56) of the finished molded lidring (30) intended to be outside of the finished molded lid ring (30).